1. Field of the Invention
This invention relates to an improved process for producing stable, low pour point synthetic oils. More particularly, this invention relates to an improved process for producing low pour point, stable oils of high VI from synthetic oil feedstocks containing wax and olefinic unsaturation wherein the improvement comprises simultaneously hydrogenating and catalytically dewaxing the feedstock over a mordenite catalyst. Still more particularly, this invention relates to an improved process for the production of low pour point, high VI, stable, synthetic oils from feedstocks derived by thermally and non-catalytically polymerizing a mixture of linear C.sub.6 -C.sub.20 carbon atom monoalpha-olefins, wherein the improvement comprises simultaneously saturating residual olefinic bonds and removing at least a portion of the wax from the feedstock by contacting said feedstock and hydrogen with a hydrogen form mordenite catalyst thereby producing a stable, high VI, synthetic oil of low pour point. 2. Description of the Prior Art
It is well known that synthetic oils of high viscosity index can be produced by polymerizing straight chain monoalpha-olefins. Synthetic lubricating oils of both high VI (viscosity index) and low pour point are made by polymerizing a relatively pure, narrow-cut monoalpha-olefin having 6 to 14 carbon atoms in the chain over an aluminum chloride catalyst in the presence of hydrogen. Lube oils produced by this process generally have a VI of over 130 with a pour point of -60.degree. F. or lower which makes them especially useful for specialty service such as lubricating aviation turbines. However, both feed and production costs are relatively high with this process.
It is also known that synthetic oils having a relatively high VI can be produced by thermal, non-catalytic polymerization of a relatively broad-cut or smear of straight chain monoalpha-olefins. Such processes are disclosed, for example, in U.S. Pat. No. 2,500,166 and U.S. Pat. No. 3,883,417, the disclosures of which are incorporated herein by reference. Thus, the '166 patent teaches a method for thermally and non-catalytically polymerizing a C.sub.6 -C.sub.12 carbon atom mixture of linear or normal monoalpha-olefins while the '417 patent relates to a two-stage, thermal, non-catalytic process for polymerizing a mixture of C.sub.5 -C.sub.20 carbon atom monoalpha-olefins. Both of these processes produce a synthetic lubricating oil having a VI in excess of 100. Unfortunately, however, although synthetic lubricating oils produced by thermal, non-catalytic polymerization of these linear monoalpha-olefin mixtures have high VI's in excess of 100, they also contain considerable amounts of wax which is reflected in pour points above 0.degree. F. and they also contain olefinic unsaturation which contributes to poor oxidation stability. Therefore, these oils must be both dewaxed and hydrogenated in order to convert them into useful products.
At least two disadvantages are associated with conventional hydrogenation and dewaxing of these thermally, non-catalytically polymerized synthetic oils. In the first place, it has been found that hydrogenating these oils with conventional hydrogenating catalysts such as cobalt molybdate, nickel molybdate or nickel-tungsten on alumina significantly increases the wax content of the oil and in the second place, it is technologically unfeasible and uneconomical to solvent dewax an oil down to a pour point of -60.degree. F. or lower. Therefore, it would be a significant improvement to the art if an efficient and economical method could be found for stabilizing and dewaxing synthetic lube oils produced by the thermal, non-catalytic polymerization of mixtures of linear, monoalpha-olefins.